The first time a person has a seizure, it can be quite frightening. It helps to know what safety measures to take when a person is having a seizure. See this link for first aid instructions for a seizure.
It is important to seek medical attention after a first time seizure. Some of the causes of a seizure (infection, hypoglycemia, hyponatremia, hypokalemia) may be dangerous and may require immediate treatment. These can be evaluated by tests.
A referral to a neurologist is a good idea after a first time seizure. They will probably use EEG and MRI tests to help decide how likely another seizure will occur. Both of these tests can be normal for a person who has had a seizure. Healthy people with a single seizure and normal tests are not likely to have another seizure, and they may not need any treatment.
For safety reasons, people who have had a seizure should refrain from driving, swimming, and climbing ladders until doctors are sure it is safe to return. Different parts of the world have different laws about how long to refrain from driving.